Feast your eyes on the volcano-covered surface of Io, the innermost of Jupiter's four Galilean moons.

We've been snapping photo's of Io's stunning surface features for decades, but only recently did the US Geological Survey team up with NASA to create a detailed "global" picture of the moon; what you see here is the product of that collaboration — the first geologic map of the solar system's most geologically active object.

You might think this map — which was published on Monday by the USGS — looks similar to others that you've seen, but there are a number of things that set it apart. For instance, unlike other planetary geologic maps, Io's surface features were characterized using four separate global image mosaics, combining the very best images collected from NASA's Voyager missions with those from the Galileo orbiter. All told, this map assembles data collected over the span of almost a quarter century. [Hi res version available here]

Many people refer to it incorrectly as its "dark" side, but the far side of our moon…
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Of course, the length of time over which the global mosaics were collected presented the USGS with a significant challenge. Because Io is so geologically active, there were many instances where surface features had changed from one mosaic to the next. "Conveying information from multiple image mosaics in a single map," explained research geologist Ken Tanaka in a USGS press release, "necessitated the use of unique and complementary map symbols, colors, and feature names."

This figure [a PDF of which is available here], which helps sort out the meaning behind all the colors and shapes that you see on the map, gives you an idea of just how complex and meticulous this process must have been.

Something else that might surprise you about this map is that none of the shapes and colors you see have been used to depict impact craters. Unlike these geologic maps of the far side of the Moon, this map of Io confirms something peculiar about the surface of Jupiter's moon that astronomers have known for years: it has no impact craters. With over 400 active volcanos covering its surface, the moon is constantly being resurfaced and reshaped, not by extraterrestrial objects, but by its own rapidly acting geological activity.

You can learn more about Io and the latest, highly detailed analysis of its surface in this pamphlet, which was prepared byt the USGS to accompany the map. [USGS]